A Comparison of Ion and Electron Energization and Transport Mechanisms in the Magnetotail During Substorms

Abstract:

We report a recent study comparing electron and ion energization and transport mechanisms in the magnetotail during substorms. The simulation scheme combines global magnetohydrodynamic (MHD) modeling of the magnetosphere driven by realistic upstream solar wind conditions, with large-scale kinetics (LSK) simulations in which we calculate the trajectories of millions of test particles in the electric and magnetic fields from the MHD simulation. In particular, during a modest substorm event that occurred on February 7, 2009, we found multiple earthward propagating dipolarizations driven by reconnection outflow jets in the MHD simulation results. Ion trajectories in the ion LSK simulation show that ions that originating near the reconnection site first gained energy non-adiabatically, and then gained energy adiabatically as they “caught up with and then rode on” the earthward propagating dipolarizations. Consequently, the integrated high-energy (>25 keV) ion fluxes were enhanced where and when the dipolarizations intensified. High-speed flows in narrow channels controlled the earthward ion transport in the magnetotail due to the dominance of E×B drift. The mechanisms of non-local energization by dipolarizations and transport controlled by high-speed flows operate similarly for electrons as reported in studies of other events by Ashour-Abdalla et al. [2011] and Pan et al. [2014]. We perform an electron LSK simulation for the same February 7, 2009 event to examine these similarities.